Naturalism is the metaphysical proposition that there exists one and only one world/reality called the natural world. This natural world is one which we can explore through our senses guided by reason and the scientific method. The only constituents in this world are physical entities that act upon each other in set and repeatable patterns called the "laws of nature", that again can be discovered through the scientific method. And finally all experienced phenomena are produced by the interactions between agglomerates of these physical entities in accordance with the laws of nature.
Transformation and Emergence
One of the perennial objections to monism of any sort (naturalistic or idealistic) is
the experienced diversity of the world. The world seems to be composed of multiple diverse categories of phenomena. How can a single substance ontology possibly account for so much diversity? The naturalist answer to this objection is in two parts:-
1)
Phase-Transition:-
disparate entities are observed to transform from one to the other
This is seen in the ordinary world when solid (ice) transforms to what seems an entirely different appearing entity, liquid water. It can also be seen in more fundamental chemical transformational processes like the creation of fire from wood and air and at a even more fundamental level, the transformation of elements through fusion or radioactivity. Death involves the transformation of life to non-life. The obverse, transforming the living to non-living, has only recently been successfully done in biology. While many other forms of categories have not yet been breached (non-consciousness to consciousness), naturalists would argue that that is simply yet another case where apparently disparate categories exist, but which has underlying unity in naturalism and a path from one to the other will be found in due course.
2)
Explanation of such variety through the concept of emergence
An example is how the laws of fluid mechanics (which liquid water follow) or the laws of crystal structure (which ice follow) emerge from underlying physics of H2O molecules at different energy states (given by quantum mechanics). In such cases it is said that the higher more circumscribed laws of fluids and crystals, catering to the phenomena of liquidity and solidity,
emerge from the underlying more generic laws of molecular physics under different conditions. The same can be said about biological processes in cells that emerge from the laws of organic chemistry applied to the system of macro-molecules under the specific conditions present in the cell. In these cases, the clear symbiosis of science with philosophical naturalism is seen, as science is seen to provide realistic, meaty and useful details that help to bolster the arguments about emergence which, before were one speculation among many. Several features of emergence are noteworthy:-
i)
Apparent Distinctness:- While the higher order physical theory (say fluid mechanics) and the more general theory (say molecular mechanics) cater to the same reality, they are completely different and apparently independent theories with their own theoretical terms and fully worked out mathematical relations and processes. Thus while in molecular mechanics, one is talking about individual discrete molecules, their potential and kinetic energies and the inter-molecular forces and collisions; in fluid mechanics one is talking about pressure, temperature, density and viscosity of fluid continuum.
ii)
Coarse-graining :- One moves from the more general theory to the higher order theory through coarse graining. Coarse graining is the observation that the unique states of a higher order emergent theory (and the phenomena it represents) correspond to many many distinct states of the underlying microscopic reality (and the phenomena it represents.) Thus the same "state" of liquid, given by its temperature, pressure and viscosity corresponds to millions and billions of distinct states of the microscopic configuration of the individual water molecules in the more basic description. Similarly a biological cell can be at a certain living state under many many configurations of the macromolecules that underlie its emergent properties.
iii)
Multiple Realizability :- There may be multiple ways to construct an emergent theory from a more underlying theory. Such theories are instances of "compression" where much of the details that "do not matter" in larger scales are thrown out and globally relevant features are concentrated on. But all this, is dependent on interest. Thus usefulness and elegance guides the emergent theory building.
iv)
Common Sense:- Crucially, Naturalism also contends that
all our "common-sense" view of the world are emergent in the same manner. Useful and emergent guides to reality at the macro-level we interact with it, but not necessarily fundamental. The fundamental realities need to be unearthed from the emergent common-sense view through careful observation, inference and reverse-engineering.
Together these concepts seek to advance a defense of the underlying physical unity of the world despite the observation of apparently disparate phenomena.
Does it succeed? What do you think?
